ML Wiki
Machine Learning Wiki - A collection of ML concepts, algorithms, and resources.

Java interview questions

interviews java

Java basics

  • Meaning of keywords: static, final, transient
  • Contract between equals() and hashCode()
  • Rules to create equals method (stability, transitivity, reflectivity etc)
  • Access modifiers in Java
  • Explain strictfp, volatile, transient?
  • Purpose, types and creation of nested classes
  • What does it mean that an object or a class is mutable or immutable?
  • How to make class immutable?
  • Besides “string” do you know any other immutable classes?
  • How can we replace multi-inheritance pattern in Java
  • Can interface inherit from different interface
  • Regular vs. static initialization blocks

Also

  • Length in bytes for primitive types
  • ’'’this’’’ and ‘'’super’’’ keywords
  • What different between StringBuffer and StringBuilder?
  • Difference between overriding and overloading

Exceptions

  • Checked vs. unchecked exceptions. Why would one use former or later?
  • Difference in handling of Error and Exception
  • Could we have only try and finally withouth catch
  • Cases when the finally block isn’t executed
  • What is exception handling mechanism
  • Java Exceptions API
  • How to avoid catch block?

Collections

  • General collection interfaces (Collection, Set, Map, List, Queue, SortedSet, SortedMap)
  • Interfaces extending Collection. Is Map part of Collection interface?
  • Difference between ArrayList and LinkedList
  • Difference between Stack and Queue
  • TreeSet vs LinkedHashSet
  • Internal structure of HashMap/Hashtable
  • Requirements for implementation of hashCode to achieve best performance
  • Definition and ways of resolving collisions in hash tables
  • Differences between Hashtable and ConcurrentHashMap
  • Special versions of collections. EnumSet, EnumMap, WeakHaskMap, IdentityHashMap.
  • Implementation details of about ConcurrentHashMap. Synchronization.
  • Iterator and modification of a List. ConcurentModificationException. Collections with safe iterators (CopyOnWriteArrayList/CopyOnWriteArraySet)

Java 5+ Specifics

  • What is a parameterized or generic type?
  • Can we use parameterized types in exception handling?
  • Liskov substitution principle
  • What is a wildcard parameterized type?
  • What is Autoboxing and what are its advantages/pitfalls?
  • Problems Enum type solves (comparing to “public static int” enum pattern)
  • Can we add something to List<?> ?
  • What are Annotations and which predefined by the language specification does one know (@Deprecated, @Override, @SuppressWarnings)

Multithreading

  • Thread vs Runnable, run() vs start()
  • Synchronization of java blocks and methods
  • Explain usage of the couple wait()/notify()
  • Difference between sleep and wait
  • Atomic operations
  • What does it mean Volatile keyword?
  • java.util.concurrent.*, what utils do you know?
  • Thread local, what for are they needed?
  • Does child thread see the value of parent thread local?
  • Deadlock definition plus example
  • Livelock definition plus example
  • Starvation definition plus example
  • Race condition definition plus example
  • Garbage definition plus example
  • Execution order
  • Atomicity of long and double assignment operations
  • Lock-free operations, how to create lock-free implementation of field reassignment

How to interrupt a thread

  • http://javatalks.ru/topics/36538
  • http://stackoverflow.com/questions/2020992/is-thread-interrupt-evil

Java NIO

  • What is NIO
  • What is Channel
  • What is Buffer
  • What is Charset
  • What is Selector
  • How to lock file?
  • what is NIO2 ?

Memory & GC

  • Memory model in JVM
  • How does virtual space divided in Java?
  • What difference between float and BigDecimal. How they store the data?
  • Java object references
  • What is deep copy of a Java object?
  • Disadvantages of setting heap size too high
  • What are utilities for JVM monitoring? What is Jconsole?
  • How to force GC be executed?
  • Garbage collection principles
  • What are memory leaks?
  • Are memory leaks a problem in Java?
  • What is variable shadowing
  • How would you monitor JVM
  • How would you monitor how GC behaves during program execution
  • Name few GC implementations (Serial, Parallel, ParallelOld, ConcarentMarkAndSweep, G1) describe major differences

Unit testing

  • Libraries that help to writing unit tests
  • EasyMock and Mockito usage
  • Junit. What is this tool for?
  • What are features of Junit? Please explain Junit Theories
✏️ Edit on GitHub